RV-9 Maneuvering Speed

[TThurston]

I notice that the maneuvering speed listed for the RV-9 in the table http://www.vansaircraft.com/pdf/speeds.pdf is 118, while it's 142 for the -7 and -8 and 144 for the -10. This makes me wonder. Why is it that much different? Is it significant in actually flying a -9?

 

[kentb]

Mine maneuvers just fine at 190 mph...

I notice that the maneuvering speed listed for the RV-9 in the table http://www.vansaircraft.com/pdf/speeds.pdf is 118, while it's 142 for the -7 and -8 and 144 for the -10. This makes me wonder. Why is it that much different? Is it significant in actually flying a -9?

But I think that the VA is probably lower because the stall is lower. I think that the max loading on the wings is lower would also make VA lower. Remember we are trying to stall the wing before it bends when we set the VA.

Another way to look at it is:
On the -7 , -8 and -10 VA is 84 mph above stall.
On the -9 VA is 69 mph above stall.
On the -6 VA is 79 mph above stall.
On the -4 VA is 80 mph above stall.

Looks like the -10 has a lot stronger wing then is needed.

Kent

 

[pierre smith]

Stress

Hi guys,
The -9 is designed for around 4 g's while the -6's, -7's and 8's are built to 6G. Since Va is the max speed at which you can exert a sharp, full application of elevator or rudder, or a combination, the -9 is going to have a significantly lower Va because it's not nearly as strong an airplane as the others. At 118 MPH and a quick, full yank on the elevator, you'll be right at the G limit, around 4 g's with no damage (supposedly.. ), whereas the 142 MPH designed Va of the others will yield 6 G's or so with the same application of full, abrupt control travel, also without damage to wings/spars. Also bear in mind the longer wing of the -9 would have a higher bending load because it's span is 4 feet longer.

Regards,
Pierre

 

[John C]

Is it really that big a difference?

There is not much of a difference the way I fly. Let me explain.

First, one should use flaps up stall speed. I think the speeds noted above are for flaps down. Then, take flaps up stall speed times the square root of the design G. That should be close to maneuver speed.

The 6 G factor is at a reduced weight of 1550. That would be about 5 G at 1800.

I think we are talking about a design differenct (at gross weight) of about 4 for the 9 (probably 3.8) and 5 for the 7 and 8. Anybody have the real design numbers? CAST says 3.8 for the -8 but that is not correct for setting Va, I suspect.

The 9 has a lower Va or maneuver speed because of the 4 G design and lower stall speed. If Vs is 59, then square root of 4 x Vs is 118. For the 8, if the stall speed is 64, then square root of 5 x Vs is 142 (just an example until we get the real numbers).

I suspect Pierre pulls Gs all day long, perhaps there is a distinct difference between 4 and 5 Gs for him. For me, there is not much difference between 4 and 5 Gs. I never get close. Either one is too much for me.

From a practical standpoint either airplane is ok with me.

Aerobatics are another matter. With the low Va for the 9, you can pull a lot more Gs with less speed which makes it more difficult to get in and out of aerobatic maneuvers. ((the most important aspect of this is the 4 versus 6 G margin))

I would suggest that you not steer away from the 9 because of the maneuver speed unless you want to maneuver (as in aerobatics).

 

[Bryan Wood]

There is not much of a difference the way I fly. Let me explain.

First, one should use flaps up stall speed. I think the speeds noted above are for flaps down. Then, take flaps up stall speed times the square root of the design G. That should be close to maneuver speed.

The 6 G factor is at a reduced weight of 1550. That would be about 5 G at 1800.

I think we are talking about a design differenct (at gross weight) of about 4 for the 9 (probably 3.8) and 5 for the 7 and 8. Anybody have the real design numbers? CAST says 3.8 for the -8 but that is not correct for setting Va, I suspect.

The 9 has a lower Va or maneuver speed because of the 4 G design and lower stall speed. If Vs is 59, then square root of 4 x Vs is 118. For the 8, if the stall speed is 64, then square root of 5 x Vs is 142 (just an example until we get the real numbers).

I suspect Pierre pulls Gs all day long, perhaps there is a distinct difference between 4 and 5 Gs for him. For me, there is not much difference between 4 and 5 Gs. I never get close. Either one is too much for me.

From a practical standpoint either airplane is ok with me.

Aerobatics are another matter. With the low Va for the 9, you can pull a lot more Gs with less speed which makes it more difficult to get in and out of aerobatic maneuvers.

I would suggest that you not steer away from the 9 because of the maneuver speed unless you want to maneuver (as in aerobatics).

Thanks for this response. Sometimes I'm amazed at what can be learned on this forum.

Best,

 

[dan]

Surprised nobody has even mentioned "wing loading" yet!

 

[fodrv7]

Twist and loading

So far all the posts treat flight as if all the loads are normal in one plane.
It's as if it is all about the Elevator and the wings.

It's much more complicated than that and needs some one like Kevin H. for a thorough explaination.

Suffice to say that if you are pulling a four G loop and apply on full aileron there is a loading far more complicated than what has been discussed so far.

Max Manoeuvre Speed applies to full application of ALL the controls.

I for one would not be trying a 'Flick Roll' at that speed.

Pete.

 

[pierre smith]

Yes, it is...

So far all the posts treat flight as if all the loads are normal in one plane.
It's as if it is all about the Elevator and the wings.

It's much more complicated than that and needs some one like Kevin H. for a thorough explaination.


Pete.

You're correct Pete,
I know there is a lot more but I try to keep my answers as short and concise as possible. Fewer words y'know mate?

Regards,
Pierre

 

[John C]

Good thoughts Dan and Pete

Wing loading and maximum lift coefficient are key parts to stall speed. The higher the wing loading (or square root of wing loading) gives increases the stall speed. The wing loading of the -9 is about 14 and for the -8 is about 15. The higher max Cl gives lower stall speeds. I suspect the 9 has a higher Clmax than the 8 but don't know. Thus, the 9 has two factors that give it a lower stall speed.

Pete raises issues you need to think about. Maneuver speed is a set number with set design requirments. For example, you should be protected from a full pull on the elevator to design G at Va; or at 1 G, a full rudder or aileron input at Va. You may or may not be protected if you are pulling design Gs and add on a full (or any) aileron or rudder input. You may or may not be protected from multiple inputs (left, right, left, right...) while at Va. In short, by design, you get one input at Va - max Gs or full aileron or full rudder, but only one at a time.

The practical side is that most of us will not want to execute a rolling pull out at max Gs, at Va, and with large aileron inputs; or bang the aileron back and forth multiple times stop to stop at Va. The airplane may sustain the multiple inputs but it is not necessarily protected by design.

Va is usually associate with control inputs so the risk may be a little obscure. It is easier to recognize the risk of flying at red line in moderate turbulence. The concepts, however, are similar.

Regards, John.

 

[N916K]

I notice that the maneuvering speed listed for the RV-9 in the table http://www.vansaircraft.com/pdf/speeds.pdf is 118, while it's 142 for the -7 and -8 and 144 for the -10. This makes me wonder. Why is it that much different? Is it significant in actually flying a -9?

Maneuvering speed isn't really all that difficult of a concept. It's the minimum speed that the plane can produce lift when at it's design limit. So basically if you are at the Va speed and in turbulence the plane will stall before it's overstressed.